Flat lamp for emitting lights to a surface area and liquid crystal display using the same

ABSTRACT

A flat lamp for emitting light to a surface area of a liquid crystal display device includes a bottom having a channel uniformly crossing an entire surface of the bottom, an arc-discharging gas is disposed within the channel, a cover disposed upon an upper junction surface of the bottom, the cover is coated with a fluorescent material, and an electric field generating means for generating an electric field, wherein the electric field generating means is placed along opposing lateral sides of the channel.

This is a divisional of application Ser. No. 09/893,988, filed on Jun.29, 2001 now U.S. Pat. No. 6,765,633.

This application claims the benefit of Korean Patent Application No.2000-64335, filed on Oct. 31, 2000 in Korea, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flat lamp for emitting light to asurface area, and more particularly to a liquid crystal display using aflat lamp for emitting light to reduce delay time for lamp turn-ondespite low voltage and to extend life-span of the lamp.

2. Background of the Related Art

Generally, lamps are classified into two categories according to theprinciples of generating light used as a light source: glow lamps andfluorescent lamps. A flat lamp belongs to the fluorescent lamps categorysince the flat lamp generates visible light rays by fluorescence inwhich ultraviolet rays produced by glow discharge within the lampstimulate fluorescent materials.

Presently, flat lamps are implemented as light sources for liquidcrystal display (LCD) devices. Since LCD devices are non-luminous anddisplay images by controlling the amount of light transmitted through aliquid crystal layer, LCD devices need additional light sources, i.e.,backlight assemblies, for displaying images.

Exemplary light sources used for backlight assemblies may be classifiedinto different categories: a point light source of a white halogen lamp,a linear light source of a fluorescent lamp, a plane light source of anelectro-luminescent (EL) device or light emitting diode.

However, the light source used in conventional backlight assemblies is alinear light source using a cold cathode fluorescence lamp (CCFL) thatrequires additional features such as a light guiding plate, a diffusionplate, and a prism sheet, for example, for producing a uniform plane oflight to a display surface.

An exemplary solution to solve the above problem is a flat lamp enabledto uniformly emit light to a surface area a planar light source.

One example of a flat lamp for emitting light to a surface area isdisclosed in U.S. Pat. No. 5,777,431, which is explained hereinafter.

FIG. 1 shows a plan view of a flat lamp for emitting light to a surfacearea according to U.S. Pat. No. 5,777,431, wherein the cover is omitted.

As shown in FIG. 1, a volute channel 6 is formed by an internal bulkhead3 and an external bulkhead 2, wherein the internal bulkhead 3 has a sameheight as the external bulkhead 2 from a rectangular bottom 1. A cathode4 emitting electrons is placed at an end of the internal bulkhead 3 thatadjoins with the external bulkhead 2. An anode 5 is disposed at a centerportion of the bottom 1 and a gas is injected into the channel 6 forarc-discharging. The volute channel 6 has a spiral shape that terminatesat a center portion of the bottom 1, whereby electrodes emitted from thecathode 4 travel toward the anode 5 in a counterclockwise direction.

In the flat lamp of FIG. 1, an electric field is generated when anelectric potential is applied between the cathode 4 and the anode 5,whereby electrons are emitted from the cathode 4 to the anode 5.Accordingly, the electrons emitted from the cathode 4 migrate along thevolute channel 6 and emit ultraviolet rays as a result of impacting withthe arc-discharging gas. The ultraviolet rays then stimulate thefluorescent material to produce a glow discharge, thereby producingvisible rays. Namely, the visible rays are emitted through the cover(not shown in the drawing) that is located at the tops of the internalbulkhead 3 and the external bulkhead 2 and disposed to overlie theentire surface area in which the channel is formed. As mentioned above,the flat lamp is used as an independent illuminator and as a backlightassembly when placed at a rear portion of a LCD device panel.

Unfortunately, the flat lamp has the cathode 4 and the anode 5 disposedat opposite ends of the volute channel 6. Accordingly, the flat lamprequires a long response time for producing visible light during theturning-on interval and requires a high voltage for sufficientluminescence. Such a high voltage inevitably reduces the life-span ofthe electrode of the cathode 4 and the anode 5, and hence, reduces thelife-span of the flat lamp. Moreover, the total length of the volutechannel 6 ultimately limits the total size of the lamp.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a flat lamp foremitting light and a liquid crystal display using a flat lamp thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art.

An object of the present invention is to provide a flat lamp foremitting light to reduce delay time for lamp turn-on despite low voltageand to extend the life-span of the lamp.

Additional features and advantages of the invention will be set forth inthe description that follows and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a flat lampincludes a bottom having a channel uniformly crossing an entire surfacethereof, an arc-discharging gas within the channel, a cover disposedupon an upper junction surface of the bottom, the cover coated with afluorescent material, and an electric field generating means forgenerating an electric field, wherein the electric field generatingmeans is placed along opposing lateral sides of the channel.

In another aspect, a liquid crystal display device includes a LCD panel,a backlight assembly disposed adjacent to the LCD panel, wherein thebacklight unit includes a bottom having a channel uniformly crossing anentire surface thereof, an arc-discharging gas injected into thechannel, a cover disposed on an upper junction surface of the bottom,and an electric field generating means for generating an electric field,wherein the electric field generating means is disposed along opposinglateral sides of the channel.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 shows a plan view of a flat lamp for emitting lights to a surfacearea according to the prior art;

FIG. 2 shows a plan view of a flat lamp for emitting lights to a surfacearea according to an embodiment of the present invention;

FIG. 3A shows a bottom of a flat lamp for emitting lights to a surfacearea according to an embodiment of the present invention;

FIG. 3B shows a bottom of a flat lamp for emitting lights to a surfacearea according to an another embodiment of the present invention;

FIG. 3C shows a bottom of a flat lamp for emitting lights to a surfacearea according to another embodiment of the present invention;

FIG. 4A shows a cross-sectional view of a channel of a flat lamp foremitting lights to a surface area along a line I-I′ in FIG. 3A;

FIG. 4B shows a cross-sectional view of another channel of a flat lampfor emitting lights to a surface area;

FIG. 5 shows an assembly view of a flat lamp;

FIG. 6 shows a wire soldering portion of a flat lamp;

FIG. 7 shows a flat lamp for emitting lights to a surface area accordingto another embodiment of the present invention; and

FIG. 8 shows a LCD device in which a flat lamp for emitting lights to asurface area is applied according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, examples of which are shown in the accompanyingdrawings. Where possible, the same reference numerals will be usedthroughout the drawings to refer to the same or like parts.

FIG. 2 shows a plan view of a flat lamp for emitting lights to a surfacearea according to an embodiment of the present invention.

Referring to FIG. 2, the flat lamp comprises a rectangular-shaped planarcover 20 of which a rear side is coated with a fluorescent material toproduce surface light, a bottom 10 that corresponds to the cover 20 andhas a channel 12 into which an arc-discharging gas is injected, anelectric field generating means 30 placed at opposite sides of thechannel 12 to form an electric field, and a connector 40 for applying anexternal power supply to the electric field generating means 30. Thechannel 12 is a single connecting curve bent several times to cross anentire surface of the bottom 10 to provide a single open surface. Anupper surface of the bottom 10 couples with a rear surface of the cover20. The cover 20 may be formed of a glass material, a heat-resistanceresin, a metal or an oxide.

The electric field generating means 30 comprises a pair of cathode andanode electrodes placed along opposite sides of the channel 12 to reducethe formation time of the electric field. Although FIG. 2 shows theelectric field generating means 30 comprising wires, it mayalternatively comprise a film or other known electric conductorstructures. Additionally, the cover 20 may comprise glass or aheat-resistant resin in order to withstand any heat generated from thechannel 12 as well as irradiate visible rays produced by the fluorescentmaterial. The bottom 10 may be formed of a metal or an oxide.

FIGS. 3A, 3B, and 3C all show a bottom of a flat lamp for emittinglights to a surface area according to the present invention.

Referring to FIG. 3A, the channel 12 is alternately formed to beparallel with long and short sides of the bottom to provide glowdischarge on a front surface of the bottom 10. For example, the channel12 extends straight from an opening surface 12 a at a lowermost longside of the bottom 10 along a rightmost short side of the bottom 10,continues along the lowermost long side and terminates at a closedsurface 12, thereby creating an “S” shape. Accordingly, the shape of thechannel 12 may not be limited to the “S” shape but may alternatively beshaped to evenly cross the entire surface of the bottom 10. Suchalternative-shaped channels are shown in FIG. 3B and FIG. 3C.

Referring to FIG. 3B, a channel 102 has a volute shape extending in acounterclockwise direction along an outermost edge of the bottom from anopening surface 102 a formed at a lowermost long side of the bottom 100and terminating at a closed surface 102 b at the center.

Referring to FIG. 3C, a channel 112 extends straight from an openingsurface 112 a at a lowermost long side of the bottom 110 along arightmost short side of the bottom 110, continues along the leftmostshort side and terminates at a closed surface 112 b, thereby creating a“zig zag” or serpentine shape.

FIG. 4A shows a cross-sectional view of the channel 12 along a line I-I′in FIG. 3A and FIG. 4B shows a cross-sectional view of another channelof a flat lamp according to an embodiment of the present invention.

Referring to FIG. 4A, wire-installing grooves 14 having a predetermineddepth may be formed on opposite sides of the channel 12 to provided forthe electric field generating means 30 (in FIG. 2). A cathode wire isformed in one of the wire-installing grooves 14 and an anode wire isformed in the opposing wire-installing groove 14. Accordingly, thepredetermined depth of the wire-installing grooves 14 must be determinedso as to not obscure the flow of electrons from the cathode to theanode. A bottom surface 16 between the wire-installing grooves 14 isformed deeper than the wire-installing grooves 14. Additionally, areflection layer may be formed on the bottom surface 16 of the channel12 (in FIG. 2) to enable effective production of light by the glowdischarge. An uppermost surface of the bottom 10 becomes a junctionsurface 18 to be coupled with the cover.

Alternatively, referring to FIG. 4B, a film 300 may be applied to forman electric field generating means installed on opposite sides of thechannel 12, thereby making the wire-installing grooves unnecessary.Instead, opposite sides of the channel 12 are coated with conductivefilms for forming the cathode and the anode. Additionally, a reflectionlayer may be formed on the bottom surface 16 of the channel 12 (in FIG.2) to enable effective production of light by the glow discharge and anuppermost surface of the bottom 10 becomes a junction surface 18 to becoupled with the cover.

Processes of assembling a flat lamp for emitting light to a surface areamay vary in accordance with the desired shapes of the channels andelectric generating means. The following description is directed towarda process of assembling a flat lamp for the case in which wires areselected as the electric field generating means in the channel shown inFIG. 3A.

FIG. 5 shows a disassembled plan view of a flat lamp for emitting lightto a surface area according to an embodiment of the present invention.

In FIG. 5, an electric field generating means is formed by insertingwires 32 and 34 for a cathode electrode and an anode electrode inwire-installing grooves 14 of a channel 12 formed at a bottom 10. Acover 20 is placed upon an upper junction surface 18 of the bottom 10and an arc-discharging gas is injected under constant pressure into thechannel 12 through the open surface 12 a. Then, the channel 12 issealed.

In FIG. 6, the wires 32 and 34 extend to a predetermined length “d”external to the open surface 12 a of the channel 12 (in FIG. 5), inwhich soldering margins 32 a and 34 a are respectively provided. Next,the soldering margins 32 a and 34 a corresponding to the wires 32 and 34are soldered with wires extending from the connector 40, whereby theassembly process is completed.

The flat lamp fabricated by this assembly process produces light by theapplication of an electric field, wherein electrons emitted from thecathode 32 travel toward the anode 34 by the application of a voltagefrom electric field generating means 30 via the connector 40.Accordingly, the electrons collide with the arc-discharging gas disposedin the channel 12 to produce a plasma that generates ultraviolet light.The ultraviolet light then stimulates the fluorescent material coated onthe cover 20, thereby producing visible rays.

Compared to the distance between the cathode and anode in the relatedart, the distance between the cathode and anode 32 and 34 isapproximately the width of the channel 12 in the flat lamp according tothe present invention, thereby greatly reducing the distance necessaryfor generating the electric field. As a result of reducing the distancebetween the cathode and anode, the initial response time forluminescence after applying power to the electric field generating means30 is greatly reduced, thereby increasing the life-span of the lamp.Furthermore, the flat lamp of the present embodiment provides alarge-sized light source that is not limited by the length of thechannel 12. The size of the flat lamp of the prior art is heavilydependent upon the channel length that is determined by the distancebetween the cathode electrode and anode electrode. Since the flat lampof the related art places the cathode electrode and anode electrode atopposite ends of the channel, the total length of the channel determinesthe overall size of the flat lamp. Furthermore, the applied voltagerequired to ignite the arc-discharge plasma is dependent upon therelative placement of the cathode electrode and anode electrode. Incontrast, the flat lamp according to the present embodiment maintains aconstant distance between the cathode electrode 32 and the anodeelectrode 34 even though the channel 12 is elongated. Accordingly, theapplied voltage necessary to ignite the arc-discharge plasma of the flatlamp of the present embodiment is significantly reduced, therebyreducing the dependence between the lamp size and the required voltage.

FIG. 7 shows a flat lamp for emitting lights to a surface area accordingto another embodiment of the present invention.

In FIG. 7, a channel 52 having an electric field generating means, i.e.,wires 32 and 34, is formed on an upper surface of a round-shaped bottom50. The channel 52 formed in the bottom 50 has a volute configurationwinding counterclockwise from an open surface 52 a at an end of acircumferential surface of the bottom to a closed surface 52 b at acenter thereof. A pair of wires 32 and 34 constitute an electric fieldgenerating means and are formed along opposite sides of the channel 52to constitute a cathode electrode and an anode electrode, respectively.Alternatively, when films are used for the electric field generatingmeans, opposite sides of the channel 52 are coated with films for thecathode electrode and the anode electrode, respectively. Additionally,other components and functions of the flat lamp are identical to thoseof the previous embodiment of the present invention.

FIG. 8 shows a LCD device implementing a flat lamp for emitting lightaccording to the present invention.

In FIG. 8, a liquid crystal display according to the present inventionincludes an LCD panel that presents image data and a backlight assemblythat is placed at a rear surface of the LCD panel to provide a lightsource. The LCD panel includes a lower glass substrate 70 on which thinfilm transistors 72 are formed, an upper glass substrate 60 on which acolor filter 62 is formed, and a liquid crystal layer 80 that isinjected between the lower glass substrate 70 and the upper glasssubstrate 60. The backlight assembly, which is installed in a lower partof the lower glass substrate 70, includes a cover 20 of which a rearsurface is coated with a fluorescent material, a bottom 10 coupled withthe rear surface of the cover and having a channel in which anarc-discharging gas is injected, an electric field generating meansdisposed along opposite sides of the channel that includes a cathodeelectrode 32 and an anode electrode 34, and a connector (not shown) thatis connected to one end of the electric field generating means to supplyelectricity.

Since a display plane of the liquid crystal display generally has arectangular shape, the corresponding shapes of the cover 20 and thebottom 10 are also rectangular. Furthermore, the shape of the channelformed in the bottom 10 may be altered in accordance with the variousembodiments described above.

Referring to FIG. 8, a diffusion plate 92, a prism sheet 94 and the likemay be formed between the LCD panel and the backlight assembly, i.e., onan upper part of the cover 20, thereby providing a light source havingmore uniform brightness and wider visible angle.

As a flat lamp for emitting light is applied to the liquid crystaldisplay having the above embodiments, high brightness is attained byproviding a uniform light source having high directiveness over anentire display surface. Moreover, the liquid crystal display may bedriven with lower power consumption by implementing a flat lampaccording to the present invention. Furthermore, the liquid crystaldisplay according to the present invention can provide a large-sizeddisplay screen by enlarging the size of a backlight assembly.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the flat lamp and liquidcrystal display using the flat lamp of the present invention withoutdeparting from the spirit of scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display device, comprising: a LCD panel; a backlightassembly disposed adjacent to the LCD panel, wherein the backlight unitcomprises: a bottom having a channel uniformly crossing an entiresurface thereof; an arc-discharging gas injected into the channel; acover disposed on an upper junction surface of the bottom; and anelectric field generating means for generating an electric field,wherein the electric field generating means is disposed along opposinginner walls of the channel, and the electric field generating means isdisposed in the channel.
 2. The liquid crystal display device accordingto claim 1, wherein the LCD panel comprises a lower glass substrate onwhich at least one thin film transistor is formed, an upper glasssubstrate on which at least one color filter is formed, and a liquidcrystal material injected between the lower glass substrate and theupper glass substrate.
 3. The liquid crystal display device according toclaim 1, wherein the electric field generating means comprises a cathodedisposed at one of the opposing inner walls of the channel, an anodedisposed at another of the opposing inner walls of the channel, and aconnector connected to an end portion of the electric field generatingmeans, wherein the connector applies an external power source to theelectric field generating means.
 4. The liquid crystal display deviceaccording to claim 1, wherein the cover is coated with a fluorescentmaterial.
 5. The liquid crystal display device according to claim 1,wherein the channel is of a serpentine shape.
 6. The liquid crystaldisplay device according to claim 1, wherein the channel is of a voluteshape.
 7. The liquid crystal display device according to claim 1,wherein the bottom and cover are round shaped.